1. Field of the Invention
This invention pertains generally to optoelectrowetting, and more particularly to single-sided continuous optoelectrowetting for droplet manipulation with light patterns.
2. Description of Related Art
Droplet-based microfluidic systems have attracted broad interest for lab-on-chip applications. Demonstrated droplet manipulation technologies are versatile and include surface acoustic wave, thermocapillary force electrowetting-on-dielectric (EWOD), dielectrophoresis (DEP), and magnetic forces. Among these systems, EWOD provides advantages in regard to fast response times, simple implementations, and large force application at millimeter to micrometer scales. EWOD-based applications, such as polymerase chain reaction (PCR) clinical diagnostics, DNA enrichment and ligation, proteomics, electronic paper, and on-chip cooling have been shown.
Conventional EWOD devices are typically implemented by sandwiching droplets between two parallel plates fabricated with one or more arrays of addressable electrodes. Actuation is achieved by digitally addressing these electrodes to induce transport from one set of electrodes to another. Certain single-sided EWOD devices integrate actuating and ground electrodes on the same substrate allowing manipulating larger droplet volumes per sample footprint, improved droplet mixing efficiencies, and flexible integration with other components such as optical detectors and external sample reservoirs.
Recent optoelectrowetting (OEW) mechanisms enable optical manipulation of droplets using light beams to overcome complex wiring and interconnect issues faced by EWOD devices using physical metal electrodes when addressing a large number of droplets in parallel on a 2D surface. Droplets manipulated in electrowetting-based devices are typically sandwiched between two parallel plates and actuated by digital electrodes. The size of pixilated electrodes limits the minimum droplet size that can be manipulated. To overcome size limitations of pixilated electrodes, a continuous optoelectrowetting device (COEW) mechanism was developed that enables continuous transportation of picoliter (pL) droplets sandwiched between two featureless and closely positioned electrodes (15 μm separation gap), one transparent Indium Tin Oxide (ITO) electrode and one photoconductive amorphous silicon electrode. However, the thick amorphous silicon layer used in COEW for matching the electrical impedance of the dielectric layer is difficult to reproduce due to large residual stress during the deposition process. Large voltage leaks in areas not covered by droplets also resulted in droplet instability issues while satellite droplets ejected from mother droplets were often observed during experiments.
Accordingly, a need exists for electrowetting droplet manipulation devices and methods which are simpler to implement while providing high accuracy.